Orbital Decay Input Form
Enter spacecraft properties, environment values, and forecast settings. The layout stays single-column overall, while the fields use 3 columns on large screens, 2 on smaller screens, and 1 on mobile.
Formula Used
This calculator uses a simplified engineering model for a near-circular orbit with atmospheric drag acting opposite the velocity vector.
- ρ is atmospheric density in kg/m³.
- Cd is drag coefficient.
- A is reference area in m².
- m is spacecraft mass in kg.
- μ is Earth’s gravitational parameter in m³/s².
- a is orbital radius or semi-major axis in meters.
This model is useful for rapid mission screening, orbital maintenance studies, and trend checks. For high-fidelity work, combine density variation, attitude changes, solar activity, and true propagator outputs.
How to Use This Calculator
- Enter the spacecraft mass, drag coefficient, and projected cross-sectional area.
- Provide the current orbital altitude and a representative atmospheric density.
- Set the target altitude if you want an estimated time to reach a lower orbit.
- Review the Earth radius and gravitational parameter fields, then edit only if your project requires custom constants.
- Choose the prediction horizon in days and submit the form.
- Read the result cards above the form, then inspect the chart for trend behavior.
- Use the CSV button for spreadsheet work and the PDF button for reporting.
Example Data Table
| Parameter | Example Value | Unit | Comment |
|---|---|---|---|
| Satellite Mass | 500 | kg | Representative low Earth orbit spacecraft mass. |
| Drag Coefficient | 2.2 | - | Typical engineering estimate for exposed surfaces. |
| Cross-sectional Area | 4.0 | m² | Reference frontal area facing drag. |
| Current Altitude | 400 | km | Common altitude for a low Earth orbit case. |
| Atmospheric Density | 3.5e-12 | kg/m³ | Illustrative density only. Real values vary strongly. |
| Calculated Decay Rate | -0.276642254 | km/day | Estimated altitude decrease under fixed density. |
| Calculated Period Change | -0.339997657 | s/day | The orbit period shortens as altitude falls. |
| Estimated Days to 350 km | 180.739 | days | Simple projection with constant decay conditions. |
Frequently Asked Questions
1. What does orbital decay rate mean?
Orbital decay rate describes how quickly a spacecraft loses altitude because drag removes orbital energy. This page reports that trend in meters per second and kilometers per day.
2. Which orbit shape does this calculator assume?
It assumes a near-circular orbit. That keeps the drag and energy model simple and makes the altitude-loss estimate easier to interpret during early engineering analysis.
3. Why do I need to enter atmospheric density manually?
Upper-atmosphere density changes with altitude, solar activity, time, and geomagnetic conditions. Entering density directly lets you test mission scenarios using your own trusted source or model.
4. What is ballistic coefficient?
Ballistic coefficient equals mass divided by drag coefficient times area. Higher values usually mean the spacecraft resists drag better and decays more slowly under the same environment.
5. Why is the decay rate negative?
A negative sign indicates the orbital radius is shrinking over time. In other words, the spacecraft is losing altitude rather than climbing to a higher orbit.
6. Can I use this for elliptical orbits?
You can use it only as a rough check. Elliptical orbits need changing velocity, changing density exposure, and more detailed propagation than this constant-density circular model provides.
7. Does the time-to-target value mean exact reentry time?
No. It is a straight projection based on the current decay rate. Real reentry timing changes as density, attitude, solar activity, and geometry evolve.
8. Which units should I use?
Use kilograms for mass, square meters for area, kilometers for altitude and Earth radius, kilograms per cubic meter for density, and meters cubed per second squared for μ.